This invention relates generally to circuit breakers and more particularly, to a wiring configuration which facilitates detecting fault current for tripping a breaker.
A typical circuit breaker includes current sensors for identifying transients in the power line current and controls for determining when to trip, i.e., open, a particular branch of the system. For example, the power line carries an input current, l.sub.in. A current sensor senses the input current l.sub.in and provides a scaled output current, l.sub.out, having a magnitude proportional to the input current, l.sub.in, but many magnitudes lower than input current, l.sub.in. The scaled output current, l.sub.out, is used to identify transients and to determine when to trip the system.
A known current sensor includes a current transformer having a core of magnetic material and one or two secondary windings. Each winding has a large number of turns of fine gauge wire evenly distributed around the core. The core encircles the power line carrying input current, l.sub.in.
In operation, an alternating magnetic flux from the power line carrying current, l.sub.in is induced in the current sensor core. A voltage therefore is induced in the secondary winding of the sensor. The signal from one secondary winding is provided to, for example, a high gain differential amplifier. The output of this amplifier can serve as a measure of the current, or for improved accuracy, the amplifier output can be supplied to a feedback winding to measure the zero-flux condition in the core. In this case, the current in the feedback winding is scaled output current, l.sub.out.
Known one pole breakers with ground-fault interruption capability contain a current transformer with two conductors passing through the transformer core, and known two pole breakers with ground-fault interruption capability contain a current transformer with three conductors passing through the transformer core. Specifically, in two pole breakers, the two power lines and the common neutral extend through the core. The power lines and neutral are arranged so that current flows through the lines in opposite directions. Such opposing current flow results in a net transformer output of zero under normal steady state operation. Any departure from cancellation of the magnetic field created by the current flows in opposing directions indicates that some current escaped to ground. If the escaped current exceeds a set point, the breaker should open. Since a perfect balance between all three currents does not imply a balance between any two, it is not possible to detect a small unbalance unless all three conductors pass through the transformer.
With such known two pole breakers, the first power line (L1) and the neutral line (N) are secured to a first subassembly, and the second power line (L2) is secured to a second subassembly. The first and second subassemblies are then connected with a plurality of optically isolated signal wires and engaged (e.g., riveted) to form the breaker. Arranging the power lines and the neutral line so that all lines extend through one current transformer creates assembly problems, and also creates sensing problems, due to the possibility that one pole line may be disconnected while the other line has a fault. It would be desirable to provide a two pole breaker configuration that is easy to assemble yet uses a current transformer to detect fault current in all the lines and whose circuitry can be powered by either pole.
Also, at least one known one pole breaker is about 3/4 inch wide and a known two pole breaker requires twice that width on the breaker panel. The width of the breaker limits the number of breakers that can be secured to one panel. It would be desirable to provide a two pole breaker that has a width of 1 inch so that more breakers can be secured to one breaker panel. As such, it would be desirable that the two pole fault detecting breaker utilize tested components already in use in 1/2 inch wide one pole breakers.
Furthermore, it would be desirable to provide a one pole fault detecting breaker that is only 1/2 inch wide.